First you need a 3d modeling program like Rhino. With that you can make any model you like although you will have to confirm it to some rules. If you got your 3d model safe it as a DXF than you'll need to get ACE whit that you can turn the DXF into an OPT.

As for good OPT makers there are a few like Darksaber, Steele, JM, Drakken, Matt, Saxman (who makes kickass models) and manymore